The invention relates to a gas bag for a vehicular occupant restraint system comprising two plies of fabric partially interwoven along their outer edges.
For producing a generally cushion-shaped, inflatable gas bag two pieces of textile material having the same shape may be joined to each other along their outer edges. Connecting the two pieces of textile material together along their outer edges is usually done by stitching, it also being possible, however, to produce the connection of two plies of fabric by interweaving them to form a sole web of material at the connecting surface area. Such a gas bag may be produced by the Jacquard weave.
When the occupant impacts the inflated gas bag and is subsequently cushioned thereby the intended energy dissipation is achieved by a controlled escape of the gas filling the gas bag. In but a few tens of a millisecond after impact the gas has already escaped almost totally from the gas bag. Should a follow-on impact occur or should the vehicle topple the gas bag is unable to offer any more protection.
The invention provides a gas bag for a vehicular occupant restraint system offering protection over a lengthy period in time amounting to several seconds which nevertheless dissipates the energy of impact to the required degree on impact and cushioning of the occupant. For this purpose the gas bag has several special features. For one thing, the plies of fabric comprising it are essentially air-tight. For another, its volume is divided into several chambers by partially interweaving the plies of fabric within the outer edges. These chambers are interconnected by at least one choked port remaining between the portions of the interwoven plies of fabric. Finally, only part of the chambers is directly inflated by an inflator, the remaining part of the chambers is indirectly inflated via the choked port. By interweaving the two plies of fabric along their outer edges an air-tight connection is achieved. Since the plies of fabric themselves are essentially air-tight the gas bag is in all air-tight to such a degree that it can provide cushioning for up to several seconds. Since dividing the gas bag into several chambers is also achieved by interweaving the plies of fabric the gas-tightness of the gas bag is not affected, unlike the usual connecting technique by stitching.
On activation of the restraint system initially only part of the chambers of the gas bag is inflated by an inflator, this being that part of the chambers which experience has shown to be expected to first come into contact with the body of the occupant. When the occupant impacts the gas bag the gas inflating it is displaced from the chambers first inflated. Via the choked passage the gas is then able to flow into the remaining chambers. The resistance to flow of the choked passage is tuned to the desired response in energy dissipation. In the case of a complex crash seqence, especially when toppling of the vehicle is involved, and when the gas bag is employed for side impact protection in the head region the occupant may impact the gas bag multiply at various positions. In this situation the gas inflating the gas bag is displaced from the chamber impacted by the occupant into the remaining chambers.